On Wed, Sep 25, 2013 at 5:33 PM, Weijie Yang <weijie.yang.kh@xxxxxxxxx> wrote: > On Wed, Sep 25, 2013 at 4:31 PM, Bob Liu <lliubbo@xxxxxxxxx> wrote: >> On Wed, Sep 25, 2013 at 4:09 PM, Weijie Yang <weijie.yang.kh@xxxxxxxxx> wrote: >>> I think I find a new issue, for integrity of this mail thread, I reply >>> to this mail. >>> >>> It is a concurrence issue either, when duplicate store and reclaim >>> concurrentlly. >>> >>> zswap entry x with offset A is already stored in zswap backend. >>> Consider the following scenario: >>> >>> thread 0: reclaim entry x (get refcount, but not call zswap_get_swap_cache_page) >>> >>> thread 1: store new page with the same offset A, alloc a new zswap entry y. >>> store finished. shrink_page_list() call __remove_mapping(), and now >>> it is not in swap_cache >>> >> >> But I don't think swap layer will call zswap with the same offset A. > > 1. store page of offset A in zswap > 2. some time later, pagefault occur, load page data from zswap. > But notice that zswap entry x is still in zswap because it is not Sorry I didn't notice that zswap_frontswap_load() doesn't call rb_erase(). > frontswap_tmem_exclusive_gets_enabled. > this page is with PageSwapCache(page) and page_private(page) = entry.val > 3. change this page data, and it become dirty > 4. some time later again, swap this page on the same offset A. > > so, a duplicate store happens. > Then I think we should erase the entry from rbtree in zswap_frontswap_load(). After the page is decompressed and loaded from zswap, still storing the compressed data in zswap is meanless. -- Regards, --Bob -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>